Many convulsant agents enhance the responses of the brainstem reticular formation (RF) to sensory stiumli before any epileptiform event appears in the EEG. Lateral geniculate, hippocampal and cortical neurons studied thus far are either minimally affected or not affected at all by convulsant administration, suggesting at least a relative specificity of this effect for the RF. Confirmation of these RF response changes in chronically prepared animals and extension of these investigations into other drug-induced, and acute focal models of seizure will indicate the generality of the RF response change. The enhancement of sensory responsiveness in RF neurons has now been observed with 5 different convulsants suggesting this effect may be a general action of convulsant agents. The site of this action of convulsants is being investigated by examining the effects of reversible (cryogenic) lesions in primary sensory nuclei, changes in RF responses to electrical stimulation in these nuclei and iontophoretic application of convulsants onto RF neurons. Results to date indicate that a major portion of the convulsant effect is exerted directly on elements of the RF. The convulsant-induced neuronal response changes may have implications for other forms of seizure, since enhancement of sensory responses is also seen in several non-drug seizure models including certain forms of human epilepsy.